1. Field of the Invention
This invention relates to a filter element for straining liquid to remove therefrom by filtration various types of foreign matter incorporated therein, which is suitable for use in a fuel filter, lubricant filter, etc., of motor vehicles, for example.
2. Description of the Prior Art
In one type of filter element for straining liquid known in the art, such as the one disclosed in U.S. Pat. No. 3,739,916, for example, the filter element has a constructional form in which filter paper is folded in half on the longitudinal center and wound in such a manner that one half portion is corrugated and the other half portion is planar.
FIG. 1 shows the essential portions of a filter element of the prior art for straining liquid, in which a corrugation W including an elevated areas and depressed areas is symmetrical with respect to the center line m. The corrugation W have bonding agent sections V of a large volume. And depressed areas at the beginning of the winding is equal to that of the elevated areas and depressed areas at the end of the winding. One of the disadvantages of the filter element of the aforesaid constructional form of the prior art is the use of a large amount of bonding agent 20 at a time the V-shaped filter paper is wound. This disadvantage is primarily attributed to the constructional form of the filter element that it is corrugated. To provide a corrugation in such a manner that the elevated areas and the depressed areas are substantially symmetrical with respect to the center line of the corrugation increases the volume of sections in which a bonding agent is stuffed. This increases the loss of pressure of the liquid flowing through the filter element, making it necessary to raise the pressure of the liquid feeding pump.
Another disadvantage, which is associated with the first disadvantage described hereinabove, is that since the sections of the filter element in which the bonding agent is stuffed have a large volume, the effective surface area of the filter paper for allowing the liquid to flow therethrough is reduced.
A still another disadvantage stems from winding of the filter paper and involves the problem that difficulties are experienced in winding the filter paper in such a manner that the pitch of the elevated areas and depressed areas of the corrugation remains constant. In particular, difficulties are encountered in winding the central portion of the filter paper which has a small radius of winding, so that the V-shape of the filter paper becomes distorted and the filter paper is difficulty wound.